Oxygen Uptake During Light Halothane Anesthesia in Man

Influence of inhalation injury on energy expenditure in severely burned children

OBJECTIVE

Determine the effect of inhalation injury on burn-induced hypermetabolism in children.

DESIGN

Prospective study comparing hypermetabolism (i.e., resting energy expenditure and oxygen consumption) in burned children with and without inhalation injury during acute hospitalization.

SETTING

Single pediatric burn center.

PATIENTS

Eighty-six children (1-18 years) with ≥40% total body surface area burns were stratified to two groups: no inhalation injury and inhalation injury.

INTERVENTIONS

None.

MAIN MEASUREMENTS AND RESULTS

Inhalation injury was diagnosed based on bronchoscopic evaluation. At admission, PaO2:FiO2 ratios (an index of respiratory distress) were significantly higher in patients with no inhalation injury than in patients with inhalation injury. No differences were detected in resting energy expenditure or percent of the predicted basal metabolic rate between groups. Additionally, oxygen consumption did not significantly differ between groups.

CONCLUSIONS

Inhalation injury does not augment the burn-induced hypermetabolic stress response in children, as reflected by resting energy expenditure and oxygen consumption.

Neuromuscular blockade significantly decreases systemic oxygen consumption during hypothermic cardiopulmonary bypass

The design limits of cardiopulmonary bypass (CPB) equipment and the performance characteristics of membrane oxygenators may place the patient with a very large body surface area at risk for incurring an oxygen debt during CPB. The influence of resting muscle tone on systemic oxygen consumption (VO2) during hypothermic (25 to 28 degrees C) nonpulsatile CPB was calculated using the Fick equation prior to, and following, neuromuscular blockade (pancuronium, 0.15 mg/kg, n = 10; or succinylcholine, 1.5 mg/kg, n = 7). During hypothermic CPB, initial VO2 was 70 +/- 30 mL/min/m2, which was significantly reduced (by 30%) to 49 +/- 13 mL/min/m2 after onset of neuromuscular blockade, with a concomitant increase in mixed venous O2 saturation from 73% +/- 18% to 83% +/- 14%. Choice of muscle relaxant did not influence the change in VO2. With succinylcholine there was a return of VO2 to control values with recovery of neuromuscular function. This study demonstrates that in the unconscious and unmoving patient during hypothermic CPB, administration of muscle relaxants to achieve complete neuromuscular blockade can significantly reduce systemic oxygen consumption.

Experimental and clinical tests of the oxyconsumeter: a new oxygen uptake monitor

The prototype of a microprocessor controlled oxygen uptake monitor oxyconsumeter developed by Draegerwerk AG, Luebeck, FRG, has been tested. The measuring accuracy of this device was assessed with laboratory bench experiments utilizing both the nitrogen dilution technique and the hydrogen combustion technique to simulate oxygen uptake (VO2). The correlation coefficient between the simulated and the measured VO2 values was 0.9989 (p less than 0.05, n = 115). The average relative error of the VO2 values was -3.32% +/- 3.88% when breathing 21 vol% oxygen and -5.58% +/- 4.53% for 70 vol% oxygen (percent of reading). This was within the range given by the manufacturer (+/- 5% for 21 vol% to less than 40 vol%, +/- 10% for 40 vol% to less than 70 vol%) with few exceptions. Furthermore the oxyconsumeter was used in clinical experiments to determine oxygen uptake during general anaesthesia. Oxygen uptake was monitored using a non-rebreathing system with an externally triggered expiratory valve. The difference between preanaesthetic reference values and values determined during anaesthesia averaged -24.8 +/- 20.1 ml/min/m2 oxygen. This average relative change of -16.0 +/- 11.5% was statistically significant in 11 of 15 cases (p less than 0.05).

Nutritional support in the critical care setting (Part 1)

Over the past two decades nutritional support has rapidly become an integral part of the medical care of critically ill patients. As scientific evidence accumulates supporting the important role of underlying nutritional status in determining the eventual outcome of many illnesses, aggressive nutritional intervention has become commonplace in our medical and surgical ICUs. However, nutritional support, particularly parenteral alimentation, is expensive and associated with important morbidity and even mortality. Furthermore, definite evidence of its clinical efficacy under certain specific conditions is often lacking and in need of properly done prospective studies. This review summarizes the basic principles of nutrition as applied to the critically ill patient in the clinical setting. Special emphasis is on practical considerations regarding cost, efficacy (or lack thereof), and potential advantages, disadvantages, and risk of complications of each proposed approach.

Rapid halogenated hydrocarbon toxicity in isolated hepatocytes is mediated by direct solvent effects

The toxicity of several halogenated and non-halogenated hydrocarbons (CH2Cl2, CHCl3, CCl4, C6H14, C8H10) in isolated rat hepatocytes were compared. Release of aspartate aminotransferase (AST) activity was rapid and concentration-dependent. Fractional AST release plateaued at 10-60 min following hydrocarbon exposure. Enzyme leakage at 60 min correlated with the oil/water partition coefficient (pi) of the compounds. All compounds, except n-hexane, also caused an immediate inhibition of the rate of cellular respiration. Inhibition of cell respiration also correlated with pi and was reversible. The recovery of cellular oxygen consumption was examined in detail for CCl4 and correlated with evaporation of the compound. These data suggest that acute hydrocarbon-induced injury in isolated hepatocytes is mediated by concentration-dependent direct solvent effects. Since halogenated hydrocarbons are widely used to induce general anesthesia, the clinical implications of possible direct effects by halocarbons on liver function in vivo and the potential relationship to liver injury are discussed.

Energy metabolism in anesthetized children with burns

Energy dynamics in 10 burned children were studied to determine cause and effect relationships between rates of heat production, heat loss and plasma catecholamine concentrations when thermoregulatory responses were depressed by methoxyflurane anesthesia. Rapid cooling of the burned children was due to increased heat loss during the period of anesthesia. Heat production increased significantly, although not enough to counterbalance the increased heat loss reflecting a block in central thermoregulation by general anesthesia. Mean plasma catecholamine concentrations decreased during general anesthesia as compared with baseline values. Heat production attempted to track heat loss during a period in which plasma catecholamine levels declined. An increased rate of heat loss is concluded to be primary stimulus for increased metabolic acitvity after thermal injury.

Effects of enflurane on haemodynamics and oxygen uptake with special reference to the influence of surgical stress

The influence on central haemodynamics of enflurane, in uniform anaesthetic concentration (1.5 MAC), was studied in 10 normocapnic patients undergoing upper abdominal surgery. The patients were studied awake, during anaesthesia prior to surgery, and during surgery. On institution of anaesthesia, cardiac output (QT) fell from 5.05 +/- 0.51 to 4.12 +/- 0.15 1/min and systemic vascular resistance (SVR) decreased from 2.36 +/- 0.22 to 1.93 +/- 0.18 kPa min. 1(-3). The arteriovenous oxygen content difference (AVD) did not change. On commencement of surgery, AVD diminished from 38.5 +/- 2.6 to 30.8 +/- 1.9 ml/min and QT rose to 5.82 +/- 0.46 1/min, while SVR remained unchanged. It is concluded that the fall in QT seen during enflurane anaesthesia is caused by a diminished tissue oxygen demand. It is also suggested that enflurane acts as an alpha-blocking agent.

The effect of surgical stress on haemodynamics during neurolept anaesthesia

The influence of surgical stress on haemodynamics during neurolept anaesthesia (NLA) was studied in ten patients, while they were awake, under anaesthesia prior to surgery and peroperatively. Systemic arterial, pulmonary arterial, right atrial and pulmonary capillary wedge pressures, as well as cardiac ouput (Qt), arterial oxygen content and mixed venous oxygen content, were measured. Systemic and pulmonary vascular resistances, arterial-venous oxygen content difference (AVD), oxygen consumption (VO2) and cardiac index (CI) were calculated. On institution of anaesthesia, CI fell from 2.8 +/- 0.1 1/min-m2 to 2.5 +/- 0.2 1/min-m2 and systolic arterial pressure (SBP) fell from 13.4 +/- 0.5 kPa to 10.2 +/- 0.3 kPa. During surgery CI rose to 3.3 +/- 0.1 1/min-m2 and SBP rose to 15.7 +/- 0.6 kPa. Prior to anaesthesia, AVD was 40.2 +/- 0.2 ml/l. Under anaesthesia prior to surgery, AVD did not change, but VO2 declined from 207 +/- 13ml/min to 171 +/- 10 ml/min. During surgery, AVD fell to 30.5 +/- 0.3 ml/l, while VO2 remained unchanged. It is concluded that NLA has a direct metabolic depressant effect and, in association with surgery, is accompanied by hyperkinetic circulation.

Changes in oxygen consumption induced by fentanyl and thiopentone during balanced anaesthesia

Changes in whole body oxygen consumption due to bolus infusions of fentanyl and thiopentone given during "balanced anaesthesia" have been examined in 17 patients. It has been shown that fentanyl causes an average decrease in oxygen consumption of 4.9, 8.4, and 5.2 per cent at 5, 10 and 15 minutes after its infusion. Thiopentone causes an average decrease of 7.0, 8.8, and 1.9 per cent at 5, 10 and 15 minutes after infusion. It is believed that the effects of fentanyl and thiopentone on oxygen consumption are caused mainly by decreases in cerebral and myocardial oxygen consumption.

Cardiorespiratory function during thoracic anaesthesia: a comparison of two-lung ventilation and one-lung ventilation with and without PEEP5

Previous studies have shown that, in patients undergoing thoracic surgery, a relatively high positive end-expiratory pressure (PEEP of 10 cmH2O = PEEP10) has no beneficial effect on oxygenation during one-lung ventilation (OLV). In the present investigation, cardiorespiratory function was examined in 11 patients intubated endobronchially and undergoing thoracotomy. Comparison was made between two-lung ventilation (TLV) and OLV and between zero end-expiratory pressure and PEEP5 during OLV. Cardiac output was determined to obtain information of the total oxygen delivery (cardiac output times arterial O2 content. The change from TLV to OLV was accompanied by a marked fall in PaO2 and a marked rise in shunt, whereas no significant change was observed in mean cardiac output. Oxygen delivery also remained unchanged due to relatively small decrease in SaO2 (arterial oxygen saturation) and maintenance of cardiac output. The application of PEEP5 during OLV produced no significant changes in these parameters. The findings in individual patients demonstrated the relative importance of cardiac output in determining oxygen delivery during OLV. A significant negative correlation was found between inspiratory airway pressure and cardiac index during OLV.